An effective geotextile is one that provides separation to preserve the aggregate base and maintain the designed structure and load-bearing capacity of the road. It helps prevent failure of the base and therefore the pavement by allowing the passage of water and preventing fine soil from mixing with the base. Light-use roads are usually constructed with thinner than required pavement thickness; these construction methods result in damage from the occasional passes of heavy delivery trucks or dumpsters, especially when the road is wet. Complete replacement of faulty asphalt or concrete sections using geotextiles to maintain the base and provide drainage is the most effective and permanent corrective action.

Where the subgrade consists of coarse soils e.g. sands and gravels, the geotextile acts as a separator between the subgrade and the ballast. The subgrade, under the effect of pressure and vibration from trains passing overhead, is prevented from working its way up into the large voids between the rail ballast stones and conversely, the ballast stones are prevented from working their way down into the soil subgrade. Without a geotextile in place, progressive settlement of the track could occur resulting in loss of track alignment and increased maintenance requirements. The pores in the geotextile are small enough to block the passage of fine sand and very coarse silt but large enough to allow the transmission of groundwater for pore water pressure relief.

Erosion protection structures or armor systems dissipate the hydraulic forces that cause erosion, and they preserve the subgrade soil or fill soil behind it. A geotextile is required between the subgrade soil and the rip-rap, gabions or pre-cast blocks to prevent piping and erosion of the soil while allowing the free passage of water. The primary function of the geotextile in erosion control is filtration to minimize erosion of the subgrade soil behind the armor system. Geotextile offers a combination of properties that make it ideally suited for permanent erosion control applications: Permittivity allows drainage Non-woven, thermally bonded fiber structure minimizes the piping and erosion of subgrade soils Tough, strong and durable Easy installation Made of polypropylene, which resists rot, mildew, microorganisms and chemicals Geotextile’s tensile strength, puncture resistance, tear resistance, opening size and hydraulic properties make it anideal filter fabric for permanent erosion control systems. The primary design requirement of apermanent erosion control system is the development of a graded aggregate filter layer in the subgrade soil. Geotextile resembles a well-graded aggregate filter. Geotextile provides an effective filter structure since it has both high permeability and the ability to retain soil particles adjacent to it, which minimizes the piping of subgrade soils and reduces fine particles from entering the watercourse.

Geotextiles are widely used for drainage in earth and construction works. In the EN ISO standards the drainage function is defined as ”The collecting and transporting of precipitation, ground water and/or other fluids in the plane of the geotextile”. In other words, it is the ability of the geotextile to drain fluids on its own, meaning that it is not part of a drainage system, but is the drainage system itself. The drainage function is often confused with the filtration function. When a geotextile is part of a drainage system, where it is used to separate a soil and a coarse-grained drainage layer, the function is filtration.Usually, the installation strains are limited and use does not apply significant mechanical strains to a drainage geotextile. Consequently, high mechanical strength is not required, whereas hydraulic properties are decisive for the overall performance of the entire construction, with the water flow capacity in the plane of the geotextile being the most important.

Synthetic drainage in natural turf applications is implemented below the sand profile. A filter fabric allows for the evacuation of water while holding the profile in place, the drainage infiltration rate is governed only by the permeability of the profile. In addition, the filter fabric creates a better perched water table for optimal turf growth which could lead up to a 75 percent reduction in the frequency of irrigation.